Indexable inserts made with hard wear resistant material such as cemented tungsten carbide cannot be successfully provided with sharp square corners located on the axially centerline of a center cutting end mill since high pressure chip loading at the center with zero or near zero cutting speed results in immediate corner breakage; likewise, if the radial cutting edge extends over center so that the sharp cutting corner is moving backwards, the backward drag on the sharp corner results in immediate corner breakdown. Accordingly, indexable insert end mills have generally been confined in use to counterboring operations or to side cutting where the center corner problem is not critical or is entirely absent.
The most pertinent known prior art is as follows:
U.S. Pat. Nos. 3,125,799, 3,540,323, 3,158,922.